Definitely depends on the spell we're talking about when it comes to chaos. As far as PoB numbers go anything in the 30-40k range with blight (before wither/blight threshold jewels) is fine. A lot of blight's damage comes from curses though so once you start getting to the guardian/shaper level you're going to start having issues, but most people go into these sorts of builds knowing that about curses. On the more extreme end I was able to get ~60k dps (again before wither/blight threshold), and ~40k dps against shaper with the reduced curse effectiveness, which ends up being what 800k dps against shaper at maximum stacks?
If you're playing blight with death's oath you'd have to lose more than 4k blight dps for the single target to be affected.
Self cast Dark pact is much easier to reach 800k+ shaper dps, but comes with the downsides of the degen and in general isn't as easy to build properly as far as killing bosses go, but I think it's really underrated if you do something like make a trickster to maintain the degen while mapping/killing map bosses, but taking it further than t15 is where you start running into issues. It's probably actually a really good build this league since there will be lots of powerful mobs during mapping situations, and the extra density will let the trickster ascendancy regen/% of life gained on kill be taken fully advantage of.
If you can somehow deal with the degen from dark pact it's going to end up being the best as far as single target goes, I've been able to reach ~1.4m+ shaper dps before, but it was kind of meaningless because the extra life regen/leech you get from not using makes it feel inconsistent during bosses. Whereas with blight you're getting a bunch of defensive layers so the dps tradeoff is worth it. The in-game currency is available at the professional online gaming house. The interested gamers can poe currency purchase from those professional online gaming houses in the most affordable cost.